WHEW! Now that you've wrangled your patient dog for [possibly] hours worth of fittings, the simple part is upon you! Sewing this thing together will be a piece of cake compared to draping on a moving target!
Let's start by making some zippered pockets. Since the kangaroo-style pockets on either side of the zipper are going to sit on you dog's back with the pocket openings facing down, I wanted to add zippers to them so that your pup can put all of their important things in them without anything falling out.
Start by using your stitch ripper (or scissors) to undo the stitching on the ends of either end of the pocket. Pin your 7” zipper in place onto the edge of the existing pocket opening. Sew into place.
Pin the other side of the zipper to the body of the coat. Sew into place. Repeat for other pocket.